It is commonly known that the position or attitude of a boat in the water impacts the boat's performance. If the front or bow of the boat is riding too high or too low more power is required to propel the boat than if the boat were positioned in the water more horizontally or level, with relation to the plane of the water. There exists an attitude angle or level plane that provides an optimal function and economy for the moving vessel. This optimal attitude varies with the speed of the boat. When the boat is traveling at a desirable level or attitude in the water it is often referred to as being "on plane" and when the boat is not in the desirable level plane or attitude angle, it is referred to as being "off plane."
Each different exterior or hull design will go on plane at a different and particular speed, specific to that hull. When the boat slows down it will go off-plane at a slightly lower speed than the speed it went on plane. There is always an "off-plane to on-plane" speed and a slightly slower "on-plane to off-plane" speed.
The adjustments that are made to obtain this proper attitude of the moving boat are often referred to as trimming the boat. A trim tab or plate is one type of device used to accomplish the trimming of the boat to the desired level plane. Most often a pair of trim tabs are utilized and positioned typically to the left and right of center on the transom of the boats.
Trim tabs typically are hinged, pivoting, planar surfaces that are mounted at the back of a motor-powered boat, on the transom of the boat. Trim tabs are mounted to the transom at the water level, for water engagement with their planar surface.
Trim tabs are positioned, relative to the hull, and relative to the transom of the boat on which they are mounted. Trim tabs are variable in position so as to change the attitude of the hull of a moving boat in response to the speed of the boat to obtain the desired level plane. Trim tabs typically pivot about a horizontal axis such that their planar surfaces are either raised or lowered to engage the moving water in different ways.
Trim tabs provide several useful functions as a result of being able to change the attitude of a moving boat's hull. These include such things as increased speed, improved economy of fuel consumption and engine efficiency, as well as, improved forward visibility. Additionally trim tabs allow adjustment of the boat's attitude to a more level position that is safer or more comfortable to the boat's occupants, and a reduced time and energy requirement for the boat to get on plane.
In most cases, adjustment of the trim tabs is assisted or accomplished by electrical or hydraulic power or a combination of the two. Trim tabs are controlled in the typical case by a pair of switches, one for each trim tab.
On small to moderate size vessels, typically 9 to 20 feet, manually operated or fixed position trim tabs have been effective in setting the planing angle. The problems encountered in the trimming process are significant due to constantly changing conditions. Automatic trimming is desirable because of the constantly changing conditions which affect the trim or attitude of the boat, such as, changes in load, speed and sea conditions.
While trim tabs are widely used and significantly contribute to proper control of power-boat attitudes as they move over the water, a number of shortcomings and problems are present in trim-tab systems of the prior art.
One problem is when the operator has no knowledge or insufficient knowledge of the positions of the trim tabs or the rate of their movement during adjustment. The trim tabs should be positioned differently during different operational conditions and uses of the boat. It can be difficult for many boat users to adjust the tabs for optimal performance.
Small vessels, often don't have room, design or electricity necessary to accommodate hydraulic/electric systems for automatic trimming. Small boats have either foregone the use and advantages of trimming devices or have used fixed trim tabs which have further undesirable characteristics. One example being, once boat is up on plane, then the fixed position of the trim tabs creates drag, which defeats their purpose.
There is still a need for automatic attitude adjustment of powered boats underway.